Since the invention (Patent Document 1) of the originator C. W. Musser, various inventions of wave gear devices have been proposed up to the present by many researchers, beginning with Musser himself and including the present inventors. There are also various inventions relating merely to the tooth profiles of these devices. For example, in Patent Document 2, the present inventors propose that the fundamental shape be an involute tooth profile, and in Patent Documents 3 and 4, the present inventors propose a tooth profile design method for guiding the addendum shapes of both gears which make wide-area contact using a technique of approximating the meshing engagement of the teeth of a rigid internally toothed gear and a flexible externally toothed gear with a rack.
[Patent Document 1] U.S. Pat. No. 2906143
[Patent Document 2] JP 45-41171B
[Patent Document 3] JP 63-115943A
[Patent Document 4] JP 64-79448A
Commonly, a wave gear device has a circular rigid internally toothed gear, a flexible externally toothed gear disposed coaxially inside the internally toothed gear, and a wave generator fitted inside the externally toothed gear. The flexible externally toothed gear includes a flexible cylindrical barrel, a diaphragm extending in the radial direction from the rear end of this cylindrical barrel, and external teeth formed in the external peripheral surface portion close to the front end opening of the cylindrical barrel. The flexible externally toothed gear is made to deflect in an ellipsoidal shape by the wave generator, and the externally toothed gear meshes with the rigid internally toothed gear in the ends of the major axis of the ellipse.
When the flexible externally toothed gear has deflected into an ellipsoidal shape, the amount of deflection in the external teeth increases along the tooth trace direction from the side close to the diaphragm toward the front end opening, substantially in proportion to the distance from the diaphragm. As the wave generator rotates, each portion of the toothed part of the flexible externally toothed gear repeatedly deflects in the radial direction.
The degree to which methods for setting a reasonable tooth profile account for such deflecting action (coning) of the flexible externally toothed gear caused by the wave generator has been insufficient. There is at present a strong commercial demand for improvement in the load torque performance of wave gear devices. To achieve this requires a reasonable tooth profile which enables a continuous meshing engagement that accounts for tooth coning across the entire tooth trace.